Hi Boris,
The release valve, at least for that type of brake cylinder, is in the correct position (it didn't pull directly on the valve - there was a small lever extending out at right angles to it) relative to the cylinder pivot bosses. However you've placed the cylinder the wrong way round as the valve should be to the inside - towards the bottom longitudinal, not as you've got it, towards the solebar side.
Lovely build all the same!